There is a difference between radar and laser jammers. Radar jammers are illegal (these work against radar guns) and have been proven to not work.
Laser jammers are pretty effective (and are legal because the FCC cannot regular light waves). Police cannot pull you over for jamming a laser signal. But, of course, always take into account that they will probably find something else wrong with your vehicle (tint, exhaust, whatever).
Good laser jammers CAN be pretty pricey… but if you’re seriously interested, give me a PM. I can probably get you a decent discount depending on the model.